JPH0220291B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to mixing devices, and more particularly to the measurement of fluid forces acting on the impeller and shaft of a mixing device, and to a method and apparatus for controlling a mixing device in response to such fluid forces. .

The present invention is particularly suited for use in mixing devices that are susceptible to large fluid forces that may permanently bend or even destroy the mixing device impeller, particularly at the outflow or when the impeller operates near the liquid surface. Are suitable.

Hydrodynamic forces are the main mechanical forces acting on the mixer shaft. Hydrodynamic forces are generated on the impeller perpendicular to the axis of the shaft and create a large bending moment (deflection) on the top of the shaft and on the drive mechanism (particularly on the gear box of the drive mechanism that houses the flux reduction gear and drives the shaft). ). In closed tanks that have a seal through which the shaft passes, these forces can cause the seal to fail. Fluid forces are explained in detail in Chapter 17 of the book Fluid Mixing Technology by McGraw-Hill, J. Oldsue (1983). Fluid power was developed by R. J. Weetman and R. J. Weetman.
Paper Chemical Engineering Progress (1981) by N. Saltzman (RNSalyman)
June 2015, pp. 71-75).

Hydrodynamic force measurement devices required laboratory instruments such as strain gauges or strain gauge bridges connected to the impeller shaft. Electrical connections to such meters must come from the mixing device via slip rings. Optical devices responsive to light reflected from a shaft have also been used to measure shaft deflection in response to fluid forces. Since the fluid forces are greatest near the impeller immersed in the material to be mixed, the optical device must be positioned at an axis well above the surface of the material to be mixed. Since the deflections are small at these locations, the optics must be sensitive. Due to the use of slip rings and sensitive optical equipment, measurements of fluid forces have been restricted to laboratory settings. Various instruments for measuring the fluid forces mentioned above are described in detail in the publications referenced above.

It has been unexpectedly discovered, namely for the present invention, that the measurement of the motion of the drive mechanism, particularly the gearbox that drives and supports the impeller shaft, has a direct correlation with the fluid forces acting on the impeller. This finding is unexpected in that the mixing device is a complex mechanical device with a complex frequency response, so the deflection of the non-rotating parts of the device, i.e. the drive mechanism, cannot be considered to be directly related to fluid forces. It's outside. Additionally, traditional hydrodynamic force measurements are carried out by attaching the impeller to the shaft and
Along with this, we have relied on rotating instruments. Even with such instruments, measurements have been difficult in that the shaft runout under no-load conditions can be greater than the shaft deflection caused by fluid forces. Measuring fluid force in response to the movement of a non-rotating drive mechanism supported above the tank therefore represents a significant improvement and simplification. Measurements are taken at a sufficient distance from the materials being mixed. Measurements can be performed on the cover of a closed tank, thus eliminating contamination of the instrument with the materials being mixed. The output from the measuring device is useful in controlling the operation of the mixing device to prevent damage or unsafe conditions that may result from excessive fluid forces. For example, when excessive fluid forces are sensed, the speed of the impeller can be reduced, thereby reducing the fluid forces and preventing damage to the mixing device that would occur if such forces were excessive. .

Accordingly, it is a principal object of the present invention to provide an improved mixing device.

Another object of the invention is to provide an improved method and apparatus for measuring fluid forces.

Yet another object of the present invention is to provide an improved method and apparatus for controlling a mixing device in response to fluid forces.

Briefly, the mixing device according to the invention comprises:
It has a motor-driven drive mechanism connected to the shaft and having an impeller thereon. The shaft is placed inside the tank for the mixed material therein. By sensing the motion of the non-rotating drive mechanism, preferably by using a proximity gauge located near the gearbox of the drive mechanism, the device is activated in response to the fluid force of the impeller flexing the shaft. Control. A signal is generated indicative of fluid force in response to the detected movement of the drive mechanism. The motor of the mixing device is controlled according to these signals. When fluid forces become excessive, the motor can be switched to run at a lower speed or stopped. Damage to the mixing device resulting from excessive fluid forces is thus avoided and safe operation of the device is ensured.

The foregoing and other objects, features, and advantages of the present invention;
Similarly, preferred embodiments of the invention, and the best mode currently known for carrying out the invention, will become more apparent from reading the following description in conjunction with the accompanying drawings.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring specifically to FIGS. 1 and 2 of the drawings, a tank 10 is shown having a suspension mixed by an impeller 14 mounted on an impeller shaft 16. The impeller is driven by a drive mechanism 18.
The drive mechanism is made up of a drive motor 20 and a gearbox 22 gear reducer assembly. The motor is mounted in a groove 24 attached to the gear box 22 by a front plate 26.

The tank may be a closed tank with a cover 28 connected to its walls, the walls of which may be circular or straight (rectangular or square). Shroud 28 rests on a gasket 30 that is aligned with the upper end of tank 10 wall. The tank is
Approximately 5 to 70 feet in diameter or width (1.53 to 21.4
m). The tank has a wide I-shaped beam 32 that provides curved support for the drive mechanism,
It is hung by 34. The gear box 22 is fastened to the beam by bolts 36. The groove 24 mounting the motor 20 can be connected by a bolt 40 to a bracket 38 which is also tightened to the beams 32,34.

Mixer shaft 16 is cantilevered from bearings in gearbox 22 and extends through an opening in shroud 28 . The opening is closed by a sealing assembly 42.

An approach gauge 44 is mounted to a support member 48 at a fixed location near the outer surface of gear box 22 . The proximity gauge is preferably a magnetic flux density responsive gauge of the commercially available type. Preferably a range of 100 mils (100 times 0.001 inch, 0.254 cm)
gauge is used. The nose of such a gauge has a diameter of 5 millimeters. This nose is positioned approximately 50 mils (0.127 cm) from the outer surface of the gear box 22 to respond to movement (displacement) of the gear box 22. Nose and surface 46 of gauge 44
The gear box is made of metal, preferably steel, so that the distance between the nose and the surface changes the magnetic flux density in the gap between the nose and the surface. The gauge therefore provides an accurate response to the flux gap length and therefore the gear box 22.
yields accurate response of motion.

A rod 50 is attached along the axis of the shaft 16 (shaft 16
(in the axial direction opposite to the direction of) protrudes upwardly from the gear box 22. This rod is also preferably made of metal (steel). Near the top of member 50,
Another proximity gauge 52 is attached to support member 54 . Member 50 serves to magnify the movement of the gear box. Therefore, the approach gauge 52 is the same as the gauge 4.
Nose diameter larger than 4 and wide area (e.g. 1
inch (2.54mm)). Gauge 5
The two noses may be spaced apart from the sides of the rod 50, with the noses being located adjacent to the sides about one-half of said extent. The spaces mentioned above, of course, relate to non-rotating axes.

The beams 32, 34 provide a curved support that allows maximum rotational movement (fixation) of the gearbox about a curved axis 56 (see FIG. 2) intersecting and perpendicular to the axis of the shaft 16. . The gauge is perpendicular to this axis and thus, together with shaft 16, responds to rotational movement or deflection of the gear box. The unidirectional deflection due to the fluid forces acting on the impeller shaft is shown by the dotted lines for the enlarged rod 50 at shafts 16' and 50'.
It will be noted that the deflection of member 50 and the motion of gear box 22 are 180 degrees out of phase with respect to the deflection of the shaft.

Gauge 44 provides an exit signal PD1. Gauge 52 provides an exit signal PD2. These signals are used to control the mixing device by controlling the speed of motor 20 for use with the apparatus of FIG. 3 for this preferred embodiment of the invention. Other uses of the signal will, of course, be apparent to those skilled in the art.

Even if the motion of the gear box 22 does not rotate, the shaft 1
To confirm that there is a direct correlation to the deflection of 6,
A ring 58 is provided around the axis 16 on the surface 60 of the material 12 of the tank 10. This ring 5
No. 8 is machined to eliminate shaft runout when no load is applied. Another proximity gauge 62 is located near ring 58. Ring 58 and gauge 62 are shown in dash-dotted lines to indicate that they are not used in use of the device, but this is due to the deflection of shaft 16 in response to the fluid force of the impeller and the gauge in response to movement of gearbox 22. It is only shown to illustrate how a direct correlation can be established between the output of

Referring to FIG. 4, there is shown a curve showing the amplitude deviation over time of signal PD1 and the amplitude deviation over time of signal PR from gauge 62. It will be noted that these signals are essentially similar in waveform. Since the mixing device is a complex mechanical device, the dynamic response over a range of frequencies, for example up to the first limit speed of the shaft that can be signaled, also shows how these are interrelated.
FIG. 5 shows the frequency response of the signal. It will be observed that these are closely interrelated. The frequency of maximum amplitude (where the fluid force represented by the frequency indicated by cursor 64 is greatest) is the most important. These signals are very closely correlated.

The deflection of shaft 16 as indicated by gauge 62 is such that the curves of FIGS. 4 and 5 are , these are taken with their phases shifted by 180 degrees to show that they are in phase. These signals also have a DC level offset. This offset can be easily adjusted with an amplifier that magnifies these signals from the gate,
Ignoring this offset, the direct correlation between the signals will become apparent from FIGS. 4 and 5.

Referring to FIG. 3, signals PD1 and PD2 are provided to switch 66. These signals are appropriately magnified and adjusted before being applied to switch 66. Depending on the amplitude range of the fluid force, one of the signals is selected by a switch. For example, if the fluid force is relatively low, select signal PD2, otherwise PD
1 is used.

If signal PD1 is used, it is fed to two level detectors 68,70. These detectors may be threshold circuits that compare the peak amplitude of signal PD1 with a fixed threshold. The limit of the first detector 68 is the limit of the second detector 7
higher than the 0 limit. The signal fed to the detector is
It is filtered to remove artifacts, ie, noise, with high frequency components that make it look like a typical signal of fluid force. If the signal exceeds the limits of the second detector 70, it provides an output that sets the latch circuit 72. Similarly, if a signal occurs that exceeds the limits of the first detector 68, it sets another latch 74. When the latch 72 is set, the output is input to the motor speed control circuit 76 to adjust the speed to two-thirds of the operating speed during normal mixing.
decrease to When latch 72 is set, speed control responds to the output of latch 74 by stopping the motor. Therefore, excessive fluid force causes a change in motor speed to instantly reduce fluid power to prevent damage or unsafe operation of the device. For normal speed operation, latch the reset input7.
It can be restarted by inputting 2.74.

The electrical circuitry shown in FIG. 3 is implemented by a suitably programmed microprocessor which also performs other control functions of the mixing device.

From the foregoing description, it should be clear that improved mixing devices have existed that are capable of measuring fluid forces and controlling the operation of the device. Variations and modifications of the devices described herein, as well as methods of measuring fluid forces and controlling devices responsive to fluid forces, within the scope of the invention will no doubt be of use to those skilled in the art. For example, a typical device may be used for only one gate 44 or 52 rather than both. The foregoing description is therefore made in an illustrative and not a restrictive sense.

[Brief explanation of drawings]

1 is a sectional view taken along line 1--1 in FIG. 2 showing a mixing apparatus embodying the present invention; FIG. 2 is a partial plan view of the apparatus shown in FIG. 1; and FIG. In response to a signal corresponding to the fluid force of the impeller of the mixing device,
A block diagram of the electrical circuit controlling the motor of the drive mechanism of the mixing device shown in FIGS. 1 and 2, and FIG. 4 is a typical example obtained from the proximity gauge used in the device shown in FIGS. 1 and 2. A curve showing a signal,
FIG. 5 is a curve showing the frequency response of the signal shown in FIG. 10... Tank, 16... Shaft, 18... Drive mechanism, 22... Gear box, 32, 34... Beam, 4
4, 52, 62...gauge, 50...member.

Claims (1)

[Scope of Claims] 1. A system for measuring fluid force applied to the shaft of an impeller of a mixing device, the shaft of which is driven by a drive mechanism attached to a support member, the shaft of which is rotated. said system for detecting the displacement of the drive mechanism due to the action of said fluid force in a direction transverse to the axis of the shaft with respect to its normal position by means of a displacement measuring device which produces an output signal indicative of the fluid force to be measured; . 2 the displacement measuring device is representative of a proximity gauge positioned adjacent to the drive mechanism and a distance between the gauge and an adjacent portion of the drive mechanism;
and a detection device responsive to a signal from the gauge representative of the fluid force to be measured.
System by. 3. The drive mechanism includes a gear box with an impeller shaft depending within a tank, and the displacement measuring device includes a gauge located adjacent to the gear box and responsive to displacement of the gear box. System according to claim 1. 4. The system according to claim 2, wherein the drive mechanism comprises a gearbox with a housing of metallic material, and the gauge is a magnetic flux density responsive proximity gauge positioned adjacent the outer surface of the housing. 5. An apparatus for amplifying the movement of a drive mechanism, the apparatus comprising a member extending from the drive mechanism in an axial direction of the shaft, the member having a proximity gauge positioned adjacent the member. 5. A system according to claim 1. 6. System according to any one of claims 1 to 5, wherein the mixing device has a flexible support for the drive mechanism. 7. A system according to claim 6, wherein the flexible support is a beam that spans a tank of a mixing device. 8. A system according to claim 6 or 7, wherein the deflection support causes a pivoting movement of the drive mechanism about a deflection axis perpendicular to said axis, and a displacement measuring device is responsive to the amplitude of said pivoting movement. 9. the displacement measuring device is operative to detect the amplitude of the rotational movement of the gear box about the deflection axis;
9. The system according to claim 8, wherein the controller is adapted to slow down the motor or stop the motor depending on the peak amplitude of the rotational movement. 10. A system according to any one of claims 1 to 9, wherein the displacement measuring device for measuring the movement of the drive mechanism produces a signal indicative of the fluid force to be measured. 11. Apparatus for slowing down the motor of the drive mechanism when the output signal indicates a fluid force causing excessive deflection of the impeller shaft.
0 system. 12. A method for measuring the fluid force acting on the shaft of an impeller of a mixing device in which the shaft is driven by a drive mechanism attached to a support member, with respect to the position when the shaft of the impeller is not rotating. the displacement of the drive mechanism in a lateral direction relative to the axis of the shaft; detecting the fluid force from the measured value; and controlling the motor of the drive mechanism in dependence on the magnitude of the movement. 13. The method according to claim 12, wherein the measurement is made by positioning a proximity gauge adjacent to the drive mechanism and obtaining an output from the gauge that corresponds to a distance between the drive mechanism and the gauge. 14. The method according to claim 13, wherein the method comprises obtaining a signal from the proximity gauge, processing the signal and providing an output to slow down or stop the motor of the drive mechanism depending on the peak amplitude of the signal. 15. Claim 1, wherein the movement of the drive mechanism is amplified by a member extending from the drive mechanism in the axial direction of the shaft, and the movement of the drive mechanism is measured by measuring the movement of the member.
Method according to 2. 16. A method according to any one of claims 12 to 15, wherein the measurement is carried out by measuring the rotational movement of the drive mechanism about the deflection axis. 17. A method according to claim 16, wherein the measurements are taken with a proximity gauge positioned adjacent to the outer surface of a gear box forming part of the drive mechanism. 18. Claim 1, wherein the mechanism has a non-rotating metal housing, and the measurement is made by measuring magnetic flux density between the non-rotating metal housing of the drive mechanism and a fixed location adjacent the housing.
18. A method according to any one of claims 2 to 17. 19. The control according to any one of claims 12 to 18, wherein the control is effected by reducing the speed of the motor when the magnitude of the movement of the drive mechanism indicates a fluid force that causes excessive deflection of the impeller. Method according to claim. 20. The system according to claim 1, comprising means for controlling the speed of the motor of the drive mechanism when the output signal indicates a fluid force causing excessive deflection of the shaft of the vane.